Vitamin D regulates lipid metabolism in granulosa cells via the FABP3-associated PI3K/Akt pathway in polycystic ovary syndrome

OBJECTIVES: To investigate whether vitamin D (VD) affects lipid metabolism in granulosa cells in polycystic ovary syndrome (PCOS) through the FABP3-associated PI3K/Akt pathway. METHODS: PCOS rat models were established using letrozole, followed by ovarian transcriptome sequencing, which revealed significant enrichment of lipid metabolism- and PI3K/Akt signaling-related pathways and identified FABP3 as a candidate gene for further investigation. Dehydroepiandrosterone (DHEA)-treated KGN cells were used as a PCOS cell model. FABP3 knockdown/overexpression, VD treatment, and PI3K/Akt inhibition were used to investigate the FABP3-associated PI3K/Akt pathway. Lipid metabolism-related regulators, including FABP3, FASN, ATGL, PPARγ, p-PI3K, and p-Akt, as well as cell viability and proliferation, free fatty acid (FFA) levels, and perilipin-2 expression, were evaluated. In vivo validation in VD-treated PCOS rats and ovarian tissue metabolomics were also performed. RESULTS: Immunohistochemical analysis revealed increased FABP3 and perilipin-2 immunoreactivity in ovarian tissues from PCOS rats. In DHEA-treated KGN cells, DHEA upregulated FABP3, FASN, and PPARγ, downregulated ATGL, inhibited PI3K/Akt phosphorylation, elevated FFA levels and perilipin-2 expression, and reduced cell viability and proliferation. Knockdown of FABP3 largely reversed these DHEA-induced alterations. Similarly, VD treatment alleviated DHEA-induced fatty acid metabolic disorders by decreasing FABP3, FASN, and PPARγ expression, increasing ATGL expression and PI3K/Akt phosphorylation, reducing FFA levels and perilipin-2 expression, and enhancing KGN cell viability and proliferation. The protective effects of VD were abolished by FABP3 overexpression or PI3K/Akt inhibition. In vivo, VD markedly attenuated polycystic ovarian changes and reduced FABP3 and perilipin-2 immunoreactivity in PCOS rats, accompanied by decreased FABP3, FASN, and PPARγ expression and increased ATGL expression and PI3K/Akt phosphorylation in ovarian tissues. Ovarian tissue metabolomics further demonstrated that VD significantly altered lipid metabolite profiles in PCOS. CONCLUSIONS: VD ameliorates lipid metabolic dysregulation in PCOS by modulating the FABP3-associated PI3K/Akt pathway, thereby alleviating granulosa cell dysfunction and ovarian pathological changes.